How do I block websites in Firefox on Mac?

You have three free routes. Install a Firefox add-on like LeechBlock NG from addons.mozilla.org, add your sites, and it blocks them inside Firefox. Or edit the macOS hosts file in Terminal to point a domain at 127.0.0.1, which blocks it in Firefox and every other browser at once. Or run the free Focuh Mac app, which blocks at the system level during a focus session so Firefox is covered alongside Safari, Chrome, and apps. Pick the add-on for browser-only blocking, the hosts file or app for system-wide.

Does the Focuh Chrome extension work in Firefox?

No. Focuh's browser extension is built for Chromium browsers — Chrome, Brave, Edge, Arc — and isn't available as a Firefox add-on, because Firefox uses a separate extension system and store. If you're in Firefox and want Focuh-style blocking, the right tool is the free Focuh Mac app, which blocks at the operating-system level and so covers Firefox without needing a browser add-on at all. That's also how you avoid maintaining a separate blocker in every browser you use.

What's the best free Firefox add-on to block websites?

LeechBlock NG is the strongest free Firefox add-on. It's open-source, has no account, and gives you up to 30 blocksets, each with its own list, schedule, and time limit, plus delay or password gates before a block can be lifted. The trade-off is a dense settings page that takes a few minutes to configure. It's the most capable browser-level option in Firefox, but like any add-on it only blocks Firefox — not Safari, Chrome, or apps.

How do I block a website in Firefox across all browsers at once?

Block beneath the browser. The macOS hosts file maps a domain to 127.0.0.1 so it fails to load in Firefox, Safari, Chrome, and Arc together — you edit one text file instead of installing an add-on per browser. The free Focuh Mac app does the same at the system level during a focus session and adds scheduling, an attempt counter, and app blocking. Both cover Firefox automatically because they work below it, not inside it.

Can I block websites in Firefox on Mac without an add-on?

Yes. The hosts file is built into macOS — open Terminal, run sudo nano /etc/hosts, add a line like 127.0.0.1 www.example.com, save, and flush the DNS cache. The site then fails to load in Firefox and every other browser, no add-on required. For a managed experience without editing system files, the free Focuh Mac app blocks Firefox at the OS level during a session. Both avoid the per-browser add-on entirely.

Does Firefox have a built-in website blocker?

Not a general one. Firefox lets you manage permissions and block notifications or pop-ups per site, but it has no built-in feature to block a website outright for focus. You need an add-on like LeechBlock NG for in-browser blocking, or a system-level tool — the hosts file or a Mac app — to block beneath the browser. So 'block a site in Firefox' always means adding something, whether that's an add-on or an OS-level blocker.

Will a Firefox add-on block sites in Firefox private windows?

Only if you allow it. Like Chrome's incognito, Firefox runs add-ons in private windows only when you enable 'Run in Private Windows' for that add-on in about:addons. Until you do, a private window is an unblocked window. And even then, the toggle can be switched back off. For blocking that private windows can't sidestep, an OS-level block from the hosts file or the Focuh Mac app is more reliable, since it doesn't care what kind of window you open.

Should I block Firefox at the browser level or the system level?

Browser level if Firefox is the only place you get distracted and you want quick, schedulable blocking — LeechBlock NG handles that well. System level if you bounce between Firefox, Safari, and Chrome, or you'll switch browsers to dodge a block. Blocking beneath the browser with the hosts file or the free Focuh Mac app means the block holds no matter which browser or app you open, which is why most people who keep escaping end up there.

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How to Block Websites in Firefox on Mac (Free)

June 19, 20269 min readFocuh

Most blocking guides assume Chrome, which leaves Firefox users guessing. To block websites in Firefox on Mac, you can install a Firefox add-on like LeechBlock NG, edit the macOS hosts file so the block covers every browser, or run a free Mac app that blocks Firefox at the system level. This guide covers all three, free, and is upfront about one thing: Focuh's own browser extension is Chromium-only, so for Firefox the better Focuh option is the Mac app.

First, the honest part about Firefox

Firefox uses its own add-on system, separate from the Chrome Web Store. That means a lot of popular blockers — including the Focuh Chrome extension — simply aren't available as Firefox add-ons. It also means Firefox is its own island: blocking a site in Chrome does nothing in Firefox, and vice versa. If you've ever blocked a site in one browser and then reached it by opening the other, that's the gap.

So in Firefox you have two real choices: block inside Firefox with an add-on, or block beneath Firefox at the operating-system level so the browser doesn't matter. Below are both.

Method 1: a Firefox add-on (browser-level)

For blocking that lives inside Firefox, LeechBlock NG is the best free pick.

Open about:addons in Firefox, or go to addons.mozilla.org.
Search for LeechBlock NG and click Add to Firefox.
Open its options and create a blockset: add your distracting domains, and optionally a schedule or a time limit.
Save. Blocked sites now redirect inside Firefox.

LeechBlock NG is open-source, needs no account, and supports up to 30 independent blocksets with schedules, time limits, and delay or password gates. The downside is a dense settings page that takes a few minutes to learn, and the structural limit of any add-on: it only blocks Firefox. Open Safari or Chrome and the block is gone. If you want a delay-based "are you sure" nudge instead of a hard block, LeechBlock can do that too.

Method 2: the hosts file (every browser at once)

If you want a site blocked in Firefox and Safari and Chrome without installing anything, edit the macOS hosts file. It sits below the browser, so one change covers all of them.

Open Terminal and back up the file: sudo cp /etc/hosts /etc/hosts.backup.
Edit it: sudo nano /etc/hosts.

Add a line per site, below the existing entries:

127.0.0.1 www.twitter.com
127.0.0.1 twitter.com

Save with Control-O and Enter, exit with Control-X.
Flush the DNS cache: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder.

The site now fails to load in Firefox and every other browser. Add both the www and non-www version of each domain. It's free and system-wide, but manual and easy to undo — anyone can reopen the file and delete the line. Full steps and how to reverse it are in how to block websites on Mac using Terminal.

Method 3: a free Mac app (the Focuh route for Firefox)

Since the Focuh browser extension doesn't run in Firefox, the free Focuh Mac app is how you get Focuh-style blocking there. It blocks at the macOS level during a focus session, so Firefox is covered automatically alongside Safari, Chrome, Arc, and even desktop apps — without a single add-on. You add your distraction list once, start a session, and the block holds across the whole machine, no matter which browser you open.

This is the cleanest answer if you use more than one browser, because you stop maintaining a separate blocker in each. For why OS-level blocking holds where browser add-ons leak, see system-level vs browser website blocking, and for blocking that spans every browser specifically, how to block websites across all browsers on Mac.

There's a private-window angle worth knowing too. Firefox, like Chrome's incognito, runs add-ons in private windows only if you switch on "Run in Private Windows" for that add-on in about:addons — otherwise a private window is an unblocked window, the same loophole add-ons have everywhere. An OS-level block sidesteps that entirely, because it doesn't care whether the window is private or normal. If you've been reaching blocked sites through Firefox private browsing, that's the strongest reason to block beneath the browser rather than inside it.

Firefox blocking methods compared

Method	Blocks Firefox	Blocks other browsers	Blocks apps	Free	Needs install
LeechBlock NG add-on	Yes	No	No	Yes	Add-on
Hosts file (Terminal)	Yes	Yes	No	Yes	None
Focuh Mac app	Yes	Yes	Yes (during session)	Yes	App

The split is straightforward. If Firefox is your only browser and you want schedules, the add-on is enough. The moment you also use Safari or Chrome — or you'll switch browsers to dodge a block — blocking beneath the browser is the only thing that actually holds.

Which method should you pick?

Firefox is the only browser you get distracted in, and you want schedules — install LeechBlock NG in Firefox.
You want one block to cover Firefox, Safari, and Chrome with no installs — use the hosts file for your permanent list.
You use several browsers, want app blocking too, or keep switching browsers to cheat — use the free Focuh Mac app for OS-level blocking.

A common setup pairs a permanent hosts-file baseline with the Mac app for focus sessions. If your distraction is mostly in another browser, how to block websites on Mac compares every method side by side, and the best free app blocker for Mac covers the dedicated-app options.

Firefox isn't harder to lock down than Chrome — it just needs a different tool, because Focuh's extension is Chromium-only and Firefox is its own island. Block inside it with an add-on, or beneath it with the hosts file or a Mac app, and the gap closes. Get the free Focuh Mac app to cover Firefox and every other browser in one go.